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Heart
Heart
49
Physiology
Graduate
07/17/2009

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Cards

Term
What are the 3 types of cardiac muscle?
Definition
Atrial
Ventricular
Excitatory and Conductive
Term
what ion channels does cardiac muscle have?
Definition
fast Na
Slow Na/Ca
K+
Term
why is the action potential of cardiac muscle so long and why does it have a plateau, where skeletal muscle does not?
Definition
AP of skeletal muscle is caused by sudden opeining of FAST Na channels, they close quickly and repolarization occurs.
Cardiac muscle, AP is caused by opening of the same fast Na channels AND slow Ca channels (Ca-Na channels)
-these are slower to open and remain open longer
large quantity of Ca and Na flows through to interior of cardiac muscle and this maintains a prolonged period of depolarization: CAUSING THE PLETEAU in AP
also, Ca ions that enter during plateau phase activate muscle contractile, Ca ions that cause skeletal muscle contraction are from sarcoplasmic reticulum
Another reason for diff:
immediately after onset on AP permeability of cardiac muscle membrane for K decreases ALOT, this does not occur in skeletal muscle (might results from excess Ca influx). Decreased permeability decreases outflux of K during AP plateau and prevents early return of AP voltage to resting level
Term
what does the plateau in cardiac muscle cause in regards to ventricular contraction?
Definition
ventric contraction lasts much longer than in skeletal muscle
Term
cardiac wave forms: Sinus nodal fiber resting potential - not a flat line. Why?
Definition
Sinus nodal fiber is leaky to Na and Ca ions and positive charges
Term
Explain what happens in the diff phases of the cardiac AP
Definition
Na channels open, Na moves into cell, increases membrane potential, depolarization. Plateau - slow opening of slow Na-Ca channels. Opening of K channels allows diffusion of large amounts of K out of fiber and returns membrane potential.
Term

Hemodynamics

Deoxygenated blood enters heart where?

Oxygenated blood enters heart where?

Definition

Deox blood enters Right atrium via Inf and Sup Vena cava

Ox enters Left Atrium via pulmonary veins

 

Term
Where does blood go after it enters the atria?
Definition

Blood in right atrium passes the Tricuspid valve to the right ventricle. then goes through the pulmonary valve to the pulmonary artery to the lungs (lowpressure)

blood in Left atrium passes through Bicuspid/mitral valve to the left ventricle

from here the blood flows through the aortic valve, to the aorta to the body (high pressure)

Term
Why is the resting membrane potential of the Sinus nodal fiber between discharges -60 mv instead of -90 like ventricular fibers?
Definition
cell membranes of sinus are naturally leaky to Na and Ca ions and these positive charges entering neutralize intracell negativity
Term
what causes the AP in the sinus node fibers (atrial)?
Definition
resting membrane potential only -55. Fast Na channels have already become inactivated. Only the slow Na-Ca channels can open and cause the AP. So the atrial nodal AP is slower to develop than the AP of ventricular muscle
Term
Where is the SA node, AV node located?
Definition

SA: roof of rt atrium

AV: Floor of rt atrium

Term
conduction of AP through cardiac muscle: slow. Rate of purkinje fiber conduction?
Definition
much faster
Term
how are AP spread cell to cell?
Definition

intercalated discs and gap junctions

gap jxn - protein pores in intercalated discs allows ions to flow from cell to cell

Term
Skeletal vs Cardiac
Definition

Skeletal

 -Rapid rise caused by sudden opening of fast Na+ channels (close quickly)

-Repolarize quickly due to K+ efflux

Cardiac

-Rapid rise caused by fast Na channels and slow Ca channels

-Ca channels slower to open and remain open longer

-Prolonged period of depolarization causing a plateau

-Ca that enters initiates the contractile process

-little K efflux while Ca gates are open

-When Ca gates close, K efflux occurs to repolarize membrane

Term

Refractory Period

of ventricle?

Atria?

Relative refactory?

Definition

Ventricle: .25 - about duraiton of plateau

Atria: .15

Relative refract period: Can get a premature beat here

Term

Excitation contraction coupling

AP passes over cardiac muscle membrane, AP spreads to interior of fiber along?

This causes?

 

Definition

T tubules

T tubule APs act on the membrane of sarcoplasmic tubules to release Ca ions into muscle sarcoplasm from sarcoplasmic reticulum

Ca ions diffuse into myofibrils and catalyze chemical reactions that promot sliding of Actin and myosin filaments along one another

Differs from skeletal:

In additon to Ca ions that are released into the sarcoplasm from cisternae of SR, large quantity of extra Ca diffues into sarcoplasm from t tubles themselves at time of AP. Without extra Ca from t tubules the strenght of contraction would be reduced because SR of cardiac muscle is less well developed than that of skeletal and does not store enough Ca

T tubules also much larger

Strength of contraction also depends on [ ]  of Ca in the ECF because T tubules pass directly through cell membrane into extracell spaces

Term
Frank Starling mechanism. waht is it?
Definition
intrinsic ability of heart to adapt to increasing volumes of inflowing blood. The greater the heart muscle is stretched during filling, the greaters is the force of contraction and the greater the quantity of blood pumped into the aorta.
Term
the amount of blood pumped by the heart each minute is determined by the rate of ? called?
Definition
blood flow into the heart from the veins - venous return
Term
Sympathetic effect on heart
Definition
increase HR, increase force of contraction, increase volume of blood pumped, increasing ejection pressure, increased CO
Term

Adrenergic Receptors and the Heart

What kinds of receptors for pacemaker cells? What mechanism opens Na and Ca channels?

this causes?

Definition

B1 adrenergic receptors

G protein mechanism

Increases diastolic depol

increases HR

Term

B1 adrenergic receptors of myocardial cells via G protein mech activates ?

This causes?

Definition

Ca channels

provides more Ca for stronger contraction

Term
There are more ___ receptors than ___ on coronary arteries.
Definition
B2 than Alpha1
Term

what do B2 receptors do? how?

What do alpha1 receptors do?

Definition

B2: smooth muscle relaxation (vasodilation)

does this by reducing sensitivity of myosin light chain kinase to Ca-Calmodulin complex

Alpha 1 in skin, GI and Kidney results in vasoconstriction by increase [Ca] in vascular smooth muscle

Term

Cholinergic Receptors

What receptors on pacemaker cells?

How do they act? results in?

Definition

M2 muscarinic receptors

directly open K channels which makes potential more negative

Reduction of HR

Term
What happens with increased K levels?
Definition

Large increase: Heart becomes dilated, flaccid, slows HR, bradycardia (trouble repolarizing)

Small increase: Tachycardia - cells are more easily excited (potential is less negative, easier to reach threshold)

Term
what happens with decreased K levels?
Definition
cells will give up K (because ECF [ ] is low), inside of cell more negative, decreases excitability
Term
what happens in the heart with excess Ca?
Definition
decreases excitability (Ca binds to Na channels, more positive, Na can't move into cells, harder to excite)
Term

Heart Energy

Aerobic metabolism of ?

Does not tolerate anaerobic metabolism. Very sensitive to?

Oxygenated blood supplied via coronaries mostly during _________?

Venous return via ___ into right atrium

Definition

fatty acids and ketones

(some sugar)

Lactate

ventric diastole

coronary sinus

Term
Does O2 or CO2 diffuse easier?
Definition
CO2
Term

Diffusion of O2 from alveoli to pulmonary capillary blood

Why?

Definition
PO2 of O2 in alveoli = 104, PO2 of venous blood = 40 (O2 removed going through tissues)
Term

Oxygenation during Exercise

During rest most perfusion happens where in lungs?

Exercise: Hypoxia causes?

Definition

base of lungs

Vasoconstriction, blood shunts toward apex of lungs - more diffusion space

(During rest blood is oxygenated only a 1/3 of the way through the lungs)

Term

Changes in PO2

Systemic venous blood is oxygenated in the pulmonary capillaries. Why is the PO2 of arterial blood decreased a little bit?

Definition

Oxygenated blood is mixed with pulmonary shunt blood

Shunt blood is blood that was shunted past the gas exchange areas, so PO2 is only 40. When this blood mixes w/ oxygenated blood the PO2 falls to 95

Term
Oxygenated blood enters left heart and is pumped into the aorta and then to the body. What happens to the PO2?
Definition
Interstitial fluid that surrounds the tissues cells is only 40, there is a large pressure diff. O2 diffuses rapidly from the capillayr blood into the tissues. Capillary PO2 falls to 40. So blood leaving tissues capillaries and entering the systemic veins is also 40.
Term
What is the effect of Rate of Blood flow on PO2?
Definition
if blood flow to a tissue is increased, greater quantities of O2 are transported into the tissue and tissue PO2 becomes higher. If blood flwo to tissue decreases, PO2 also decreases
Term
What happens to O2?
Definition

O2 becomes H2O

-Food is stripped of H+ by dehydrogenases

-H+ is oxidized forming H2O

CO2 is relased from food substrate by decarboxylases

-dissolves into body fluids

-transported by blood to lungs

Term

PCO2- CO2 diffuses 20x more rapidly than O2

Diffusion of Co2 from peripheral tissue cells into Capillaries

Definition

Intracellular PCO2 46, Interstitial PCO2 45

CO2 diffuses from tissues into blood

Term

Alveolar CO2 Diffusion

Alveolar PCO2 = 40

Pulmonary PCO2 = 45

Definition
CO2 goes from blood to alveolus
Term

Effect of Blood flow and Metabolism on Peripheral PCO2

Decrease in blood from from normal to 1/4 normal does what to peripheral tissue PCO2?

Increasing blood flow to 6x normal decreases does what to interstitial CO2?

Definition

Increases tissue PCO2 to an elevated 60

Decreases interstitial PCO2 from 45 to 40

Term

O2 transport

what is it bound to?

what is binding dependent on?

Definition

97% bound to Hgb

3 % dissolved in fluids

PO2

Term

When PO2 is high, what happens with O2-Hgb binding?

When PO2 is low?

Definition

PO2 high - O2 binds with Hgb

Low - O2 is released from Hgb

Term

O2-Hgb Dissociation

Progressive increase in % of Hgb bound with O2 as ? Called?

Definition

blood PO2 increases

% saturation of Hgb

Term

O2 delivery

O2 sat vs O2 content. How is this not always equal?

Definition

you can have good O2 sat but low O2 content

it you only have a little bit of Hgb it doesn't take much O2 to saturate it!

Term
What is offloading of O2 affected by?
Definition

Tissue O2

Tissue CO2

pH

temp

BPG

Term
O2 delivery is relative to?
Definition

perfusion

CO

Term
what is BPG?
Definition
biphosphoglycerate - produced by RBCs to bump off O2 to be delivered
Term

Shifting Dissociation Curve

Right shift: Facilitates?

What happens to:

O2

CO2

pH

Temp

BPG

Definition

offloading of O2

Tissue O2 falls

Tissue CO2 risise

pH falls

increase in TEmp

increase in BPG

Term

shifting dissociation curve

Left Shift: facilitates:?

effects on:

pH

temp

BPG

Definition

O2-Hgb bonding

pH rises

temp decreases

decrease in BPG

Term
Bohr Effect: what does it show?
Definition
increased delivery of O2 to tissues when CO2 and H+ ions shift the O2-Hgb Dissociation Curve to the right
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